1. Field of the Invention
The present invention relates to a device for monitoring farm animals for the purpose of detecting estrus.
2. Description of the Prior Art
For economic reasons and improved genetic traits, many farm animals are bred using artificial insemination. When using artificial insemination, a method of estrus detection is employed to judge the appropriate time for insemination. Failure to properly detect estrus results in failure to conceive. In the United States, the most pressing need for an automated system for detecting estrus is in the dairy industry. Failure to conceive at the desired time results in loss of milk production, increased culling of producing animals, reduced number of calves which can be sold due to the need to replace culled animals, and other factors which have a negative economic impact. Estimates place the annual per head loss for the average dairy herd at $150.00 to $300.00 per animal.
The most common method of estrus detection employed by the United States dairy industry is to visually observe the behavior and condition of herd animals at feeding and milking times. A number of factors have been documented (see U.S. Pat. No. 3,844,273, and The Veterinary Record, July 15, 1972, pages 50-58) which can be observed visually to detect estrus in dairy animals.
Several techniques have been proposed in either the scientific literature or in patents to either automate the process of estrus detection or improve its accuracy beyond visual observation of the herd. These techniques include the use of heat mount detectors (see Kaymar, Inc. product literature, Steamboat Springs, Colo.), the use of pedometers for the measurement of movement activity (see U.S. Pat. No. 4,247,758), the use of video cameras and recorders to provide twenty-four hour observations of behavior (see Canadian Journal of Animal Science, June 1976, Volume 56, pages 291-298), the use of probes to measure vaginal impedance (see Animal Tek product literature, Boulder, Colorado), measurement of body temperature, and the measurement of milk or blood progesterone.
Heat mount detectors involve the use of a patch which is attached to the back of the animal near the tail. When an animal is in estrus, she will stand to be ridden by other animals. When an animal is ridden by another animal, a pouch located in the patch which is filled with bright colored ink bursts, indicating that the animal was receptive to being mounted and is probably in estrus. Although heat mount detectors have been shown to be effective as an aid for detecting estrus, their major limitation is that they fall off the animal too frequently and do not lend themselves to automation.
Pedometers have also been shown to provide a significant improvement over the norm in their ability to determine if an animal is in estrus, although thorough testing has not yet been performed. The obvious limitation of this technology is that a large percentage of dairy herds in the northern United States are stanchioned most of the time, limiting the degree of changes in activity which could be perceived.
Video cameras and recorders have also been shown to be effective, but they require considerable labor to review recordings and a sizable capital investment.
Measurement of body temperature has been tried as a means of estrus detection. However, changes in environmental temperature often mask changes induced by estrus and measurement of temperature by itself is considered to provide a poor indicator of estrus.
Measurement of progesterone levels is a very effective way of detecting estrus. However, the cost of such assays makes common use of this method prohibitive.
Research indicates that measurement of impedance may provide an accurate and reliable means of detecting estrus. Combining measurement of impedance with other parameters such as temperature and movement activity would very likely improve the accuracy and reliability of estrus detection.
In addition to the ability to detect estrus, research indicates that measurement of impedance may have the additional benefits of being able to detect pregnancy and the approach of parturition, and may also provide a screening tool of genital disorders.
The use of impedance for detecting estrus was first reported by Aizinbudas and Dovilitis in the journal Zhivotnovodstvo 11:68-70 in 1962. Published studies in which vaginal impedance has been measured have done so by measuring the tissue impedance when stimulated by a sinusoidal waveform of a specific frequency.
Animark of Boulder, Colorado and Animal Tek each manufacture a probe capable of measuring impedance which can be temporarily inserted into the vagina. Field trials of these devices indicate that they are relatively ineffective at detecting estrus. Frequent insertions are required in order to detect estrus, resulting in vaginal inflammation and occasionally, infection.